Prazosin Drug Classification
Prazosin is an alpha-1 adrenergic receptor blocker (alpha-1 antagonist). 1
Mechanism and Pharmacology
Prazosin is a quinazoline derivative that works as a selective postsynaptic alpha-1 adrenergic receptor antagonist. 1 This selective blockade of alpha-1 receptors distinguishes it from older, nonselective alpha-blockers like phentolamine and phenoxybenzamine. 2
The drug exerts its therapeutic effects through:
- Vasodilation via alpha-1 receptor blockade in resistance arteries and capacitance veins
- Relaxation of smooth muscle in the bladder neck and urethra
- Reduction of peripheral vascular resistance without causing reflex tachycardia (unlike direct vasodilators)
Clinical Classification Context
Within the broader antihypertensive drug categories, prazosin falls under the alpha-1 blocker class, which includes:
- Doxazosin
- Prazosin (2-20 mg daily in 2-3 divided doses)
- Terazosin
Important Clinical Considerations
This drug class is NOT recommended as first-line antihypertensive therapy. 3 Alpha-1 blockers like prazosin are associated with:
- Orthostatic hypotension, especially in older adults
- First-dose syncope (can occur shortly after initial dosing)
- Risk of Intraoperative Floppy Iris Syndrome (IFIS) during cataract surgery 1
Prazosin may be considered as a second-line agent in patients with concomitant benign prostatic hyperplasia (BPH) due to its relaxant effects on the bladder neck and urethra. 3
The drug also has off-label use in PTSD for trauma-related nightmares and sleep disturbances, where it acts centrally to reduce noradrenergic hyperactivity. 4, 5